Inherited neuropathy (IN) has a relationship with family medical history and is a congenital disease characterized by dysfunction of motor and sensory nervous systems stemming from gene mutations. Among inherited neuropathies, mention may be made of CMT (Charcot-Marie-Tooth disease), HNPP (Hereditary Neuropathy with liability to Pressure Palsies), DSS (Dejerine-Sottas Syndrome) and CH (Congenital Hypomyelination neuropathy), for example. These diseases are caused by genetically heterogeneous factors, and CMT, exhibiting the highest frequency of occurrence among inherited neuropathies, shows an incidence rate of about 1:2,500 in Europeans, and HNPP shows a frequency of occurrence of 16 people per 100,000.
CMT disease is characterized by muscle weakness and atrophy which gradually progresses primarily in peroneal muscle of the lower extremities. This disease may also manifest areflexia, distal sensory loss, pes cavus, and deafness. Onset primarily occurs in the teens, and rarely after the thirties. However, clinical phenotype and onset age of CMT are very heterogeneous and further it is not easy to perform nerve biopsy for definitive diagnosis, thus rendering accurate diagnosis and treatment difficult (Berger P., Young P., Suter U. Neurogenet. 4: 1-15 (2002)).
Recently, thanks to studies into the human genome and advanced bioinformatics, studies and research to isolate causative genes responsible for hereditary diseases and to elucidate molecular biological mechanisms thereof are now being actively undertaken throughout the world. A great deal of substantial analysis has been made on hereditary causes of CMT, which is known to be developed by hereditary factors, rather than by environmental factors. As a result, more than 10 genes are known to be involved in pathogenesis of CMT, and most of these mutations have been found to be due to Single Nucleotide Polymorphism (SNP) and duplication/deletion of a short base sequence, except for duplication/deletion of 17p11.2-p 12 1.5 Mb. Table 1 below shows inheritance mode and phenotype of important genes responsible for development of CMT known hitherto.
TABLE 1No. ofInheritanceClinicalmutationGenesLocimodephenotypefoundPMP2217p.11.2Autosomal dominantCMT1,59HNPP,DSS,DeafnessCx32XXq13.1X-linked dominantCMT1X265MPZ1q22Autosomal dominatCMT1B,99Autosomal recessiveCMT2,DSS,DeafnessEGR210p21.1-Autosomal dominantCMT110p22.1(severe),DSS, CHNEFL8p21Autosomal dominantCMT1F,24Autosomal recessiveCMT2EPRX10p13.1-Autosomal recessiveCMT1,17p13.2CMT4F,DSS
CMT is broadly classified into CMT1 due to demyelination of the myelin sheath and CMT2 due to an impairment of axon function (axonopathy). More than 50% of CMT1 is caused by a 1.5 Mb duplication in the chromosome 17p11.2-p12 region where a PMP22 (peripheral myelin protein 22) gene is located and the resulting disease is called CMT1A disease, taking the highest proportion among overall CMT disease groups. Contrary to CMT1A, HNPP is reported to be due to deletion of the same 1.5-Mb region in 70% to 100% of patients. Therefore, the presence of duplication in the PMP22 gene enables definitive diagnosis of CMT1A, whereas deletion of the PMP22 gene enables definitive diagnosis of HNPP.
HNPP is an autosomal dominant-hereditary disease accompanied by repetitive neuralgia and muscle weakness. This disease is also associated with nervous system abnormalities induced by partial thickening of the myelin sheath (tomacula) as revealed by nerve biopsy. There are few reported cases of HNPP in Korea, as compared to Western countries, and the reason is considered owing to technical problems in that the presence of tomacula should be confirmed via nerve fiber teasing, in order to make a definitive diagnosis of HNPP disease. However, as it is recently possible to easily diagnose this disease via genetic testing, it is believed that frequency of such disease cases will increase.
Since most diseases that currently receive genetic testing are diseases caused by complicated interaction between polygenic inheritance and various environmental factors, such genetic testing for these diseases simply indicates predisposition to disease pathogenesis (for example, genetic testing of hyperhomocysteinemia-associated MTHFR (5,10-methylenetetrahydrofolate reductase) and breast cancer-inducing BRC-A or BRC-B genes). However, CMT is caused by a single gene mutation, and pathogenesis thereof very faithfully follows Mendelian inheritance even though there are some differences in severity of symptoms. As such, CMT exhibits substantially direct linkage between genetic defects and pathogenesis thereof, as exhibited by Phenylketonuria (PKU) and therefore the results of the genetic testing obtained from such diseases provide a definitive diagnosis, rather than simply at presentation level of predisposition or possibility of disease development, and thus CMT is a genetic disease that is very suitable for utilization of a genetic diagnostic kit. In addition, if the etiologies of inherited neuropathies caused by single gene mutation while exhibiting strong hereditary tendency are elucidated via genetic testing, it will be possible to fulfill underlying treatment of diseases in conjunction with more accurate diagnosis. A need for early diagnosis of inherited neuropathies was not raised hitherto due to the absence of relevant treatment methods even though early diagnosis was made for such inherited neuropathies. However, it was recently published in the scientific literature and scientific journals that ascorbic acid and progesterone antagonists are therapeutically effective on CMT1A (Sereda M. W., Horste G. M., Suter U., Uzma N., Nave K.-A. Nature Genet. 9: 1533-1537 (2003); Passage E., Norreel J. C., Noack-Fraissignes P., Sanguedolce V., Pizant J., Thirion X., Robaglia-Schlupp A., Pellissier J. F., Fontes M. Nature Genet. 10: 396-401 (2004)). Therefore, if methods capable of accurately diagnosing CMT1A duplication/HNPP deletion are developed, inhibition of disease development and patient-tailored treatments may be feasible pursuant to accurate early diagnosis of diseases or diagnosis prior to onset thereof. The present invention relates to accurate diagnosis of CMT1A and HNPP, pathogenic causes of which are duplication and deletion in the chromosome 17p11.2-p12 region.
In order to examine CMT1A duplication and HNPP deletion, conventional methods have employed a southern blotting technique using radioisotopes. Recently, via DNA typing of microsatellites present in a 1.5 Mb duplication/deletion region, it became feasible to examine such chromosomal abnormalities without the use of hazardous radioisotopes. However, since markers such as D17S921, D17S955, D17S839 and D17S122, which are largely used in DNA typing, have sequences consisting of (CA)n repeat units, PCR of such markers causes severe non-specific DNA amplification due to heavy slippage, thus making it difficult to perform accurate typing of microsatellites (Mersiyanova I. V., Ismailov S. M., Polyakov A. V., Dadali E. L., Fedotov V. P., Nelis E., et al. Human Mutat. 15: 340-347 (2000)). As a result, there were disadvantages associated with necessity of utilizing radioisotopes for accurate diagnosis, and inevitable need of parent's samples for examination of patients.
Moleculargenetic studies into inherited neuropathies have been largely led hitherto by European countries, but considerable studies into such diseases are also now being actively undertaken in Japan as well as the USA and European countries since the new millennium. Yoshihara et al. (Yoshihara T., Yamamoto M., Doyu M., Misu K. I., Hattori N., Hasegawa Y., Mokuno K., Mitsuma T., Sobue G. Hum. Mutat. 16: 177-178 (2000)) and Numakura et al. (Numakura C., Lin C., Ikegami T., Guldberg P., Hayasaka K. Human Mutat. 20: 392-398 (2002)) have detected causative mutations in CMT1A duplication, PMP22, MPZ and Cx32 from about 100 Japanese CMT patients. However, there is no accurate statistical data on incidence rate of CMT diseases for Koreans and it is merely believed that situations in Koreans are similar to those of Europeans. The present invention is designed to grasp an accurate definitive diagnosis rate according to a diagnostic method by firstly accurately analyzing hereditary causes of CMT development in Korean CMT patients and their families and comparing the resulting analysis data with foreign data.